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    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
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  <body>
    <script>
      var a = 10;
      var b = 20;
      // 交换一下 a,b 的值
      var temp = a;
      a = b;
      // b = a; // 需要把 之前的 a  赋给 b
      b = temp;

      var arr = [2, 3, 5];
      // 交换3,5 两个元素的位置
      var res = arr[1];
      arr[1] = arr[2];
      arr[2] = res;
      console.log(arr);
    </script>
  </body>
</html>
